The present invention relates to the positive-displacement pumping of highly viscous materials, such as unvulcanized rubber.
The manufacture of rubber products requires the capability of extruding products while metering them quantitatively in a very accurate manner. Among the many applications which may be envisaged, mention may be made of the formulation of rubber mixes which requires accurate metering of various basic constituents, or the assembly of a finished product, such as a tire, which requires strictly defined amounts of rubber mixes to be extruded onto a rotating support.
In the latter case, the problem is further compounded owing to the fact that in this type of application extrusion is not continuous, but takes place on demand, according to a cycle whose period corresponds to the time required to assemble each manufactured article, for example each tire. It is important to gain complete control over the quantities extruded, including during the stop and start-up phases of extrusion.
To this end, it is preferable to ensure that the flow rate of extruded material depends on just one control parameter of the pump, namely, for example, the speed of rotation of a control shaft, and for it to be dependent in such a way that the flow rate is at every moment strictly proportional to the speed of rotation of the control shaft. U.S. Pat. No. 5,261,795 discloses a positive-displacement pump which, in one of its alternatives, has two pistons and non-return balls controlled by rods and a rocker. This pump meets these objectives.